This section is intended to provide a background or context to the invention recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
A hydraulic drilling apparatus has an internal, oscillating hammer that is accelerated and decelerated at high rates of speed by means of shifting media (e.g. hydraulic, pneumatic, etc.) pressure. The shifting media pressure acting on differential areas of the hammer and shuttle valve causes the movement required for oscillation. The movement of the hammer is typically driven by hydraulic or pneumatic flow in a system that has a high pressure media supply path and a low pressure return path for the shifting media entry and exit of the hammer. The media supply and return circuits typically have one or more accumulators in the supply and return paths, which are usually mounted directly onto the drilling apparatus. The accumulator is intended to dampen peak pressure surges that are inherent in media systems, as well as provide a boost of media flow to the system if the flow from the primary pump is not adequate at a given time in the hammer oscillation cycle. The accumulator typically includes a diaphragm that separates hydraulic or pneumatic fluid from the accumulator charging media (e.g., nitrogen gas).
However, certain challenges are presented in such systems. For example, nitrogen gas may leak from the accumulator to the outside environment, such as through an improperly seated charge valve. Also, most flexible diaphragms are permeable and gas can pass through them over time. Also, if the accumulator diaphragm is torn or has a hole in it, the nitrogen gas may leak into the fluid system. Further, the accumulators are charged to a specific pressure range based on a percentage of the supply and return circuit pressures. If the accumulators are over or under charged, shifting media flow may not be adequate for the proper operation of the drilling apparatus. Still further, the operator of the drill unit or service personnel can lower the media supply and return pressure of the drilling apparatus itself causing the accumulators to be out of specification in comparison to the accumulator settings.
If the charging media in the accumulators leaks into the driving media or into the outside environment, or if the accumulators are incorrectly charged, an insufficient pressure may be exerted by the accumulator. When the flow in such a system is insufficient to fill the changes in volumetric requirements, a negative pressure may occur (e.g., a vacuum) resulting in cavitation. Cavitation may cause undesirable hammer movement and speeds which may cause the hammer to over-stroke and impact other internal mechanical components ultimately resulting in overstressed parts which may lead to failures. Because the hammer is usually located at a distance away from the operator, the operator may not be aware if the accumulator(s) lose a charge or are otherwise over or under charged for providing the proper operational supply and return pressure for the hammer.